Field of the Invention
The present invention relates to a fluid containing a sulfur-containing polyalkylene glycol base oil and an antioxidant.
Introduction
Industrial fluids that are fire resistant, and particularly those that have thermo-oxidative stability, are desirable for high temperature applications such as lubricants and hydraulic fluids in steel processing and power generation. It is a continuous desire and challenge to increase the fire resistance and thermo-oxidative stability of such industrial fluids. Hydrocarbon oils, which are historically used as lubricants, are generally undesirable in such applications because of their combustible nature. Water-based lubricants offer better fire resistant properties than hydrocarbon oils but tend to be unsuitable for use in high temperature applications where water can evaporate. Anhydrous lubricants are typically needed for high temperature applications.
Conventional polyalkylene glycols (PAGs) are known as lubricant base oil alternatives to hydrocarbons and water. Conventional PAGs are PAGs that are initiated using a monol, diol or triol and reacted with ethylene oxide and/or propylene oxide to form polymers which typically have molecular weights greater than 500 g/mol and up to 50,000 g/mol. Lubricant compositions using such conventional PAGs as base oils offer favorable performance benefits as hydraulic fluids and turbine oils. Yet, conventional PAGs tend to suffer from oxidative instability unless an antioxidant is present. Therefore, as antioxidant depletes from a conventional PAG based lubricant composition the oxidative stability of the lubricant suffers undesirably.
It is desirable to identify an industrial fluid that offers fire resistant properties and thermo-oxidative stability while also offering lubricating capabilities of a PAG, especially if the performance of the lubricant base oil exceeds that of conventional PAGs so the oxidative stability of the fluid is less dependent on the amount of antioxidant present.